The present invention relates to a pneumatic drive for switching elements and control elements, for example, closures, valves, flaps, switches, signalers or the like.
The drive includes a piston which is movable in a cylinder, a piston rod which is connected to the piston and acts on the switching or control element which is to be activated, and at least one supply line for a compressed gaseous medium. This supply line charges into the cylinder from an opening near the cylinder base, and a valve is arranged in the supply line which valves closes or vents the supply line. The supply line has, between the valve and the opening in the cylinder, at least one branch line which opens into the closed end region of an annular groove provided in the cylinder. A sealing ring is received in the groove so that when the gaseous medium is discharged from the supply line to pressure the cylinder, the sealing ring is urged by the medium to seal the pressurized cylinder.
A pneumatic drive is known in which the groove which carries the sealing ring is provided in the inner cylinder wall, i.e., in the region over which the piston travels. When the cylinder is pressurized with the compressed medium, the sealing ring moves transversely of the direction of movement of the piston, and contracts against the piston. When the cylinder is relieved of pressure, the sealing ring which is of a soft rubber material is also urged outwardly, transversely to the direction of movement of the piston. The sealing ring must be suitably yielding and elastic so that it can perform these movements, and expand and contract to a sufficient extent. The gap which is opened by the sealing ring when the cylinder is depressurized is defined by the inner cylinder wall and the side wall of the piston and, consequently, has a relatively small cross section because this gap also determines the play between the piston and the cylinder wall, and it cannot be enlarged at random in view of maintaining correct guidance of the piston in the cylinder.
An object of the present invention is to provide a drive arrangement in which a vent may be formed as large as possible so that the cylinder can be quickly depressurized through the vent, without influencing the amount of play between the piston and the cylinder wall for guiding of the piston.
In addition, sliding friction developed by the sealing ring, which so far has resulted from relative motion between the sealing ring and the piston, is prevented with the object of increasing the service life of the sealing ring.
Another object of the invention is to manufacture the sealing ring of a material which is harder than the soft rubber used until now, so that it is possible to operate with higher differential pressures. This favorably influences the speed of the depressurizing process.
In accordance with the present invention, the cylinder has an annular slot which extends in a plane perpendicular to the axis of the cylinder, the slot being located in a region over which the piston travels, preferably close to the cylinder base. The slot leads from the interior cylinder space to the outside, and at least one of two annular surfaces which form the slot has the annular groove which opens toward the other annular surface and, which receives the sealing ring. The closed end region of the groove communicates with a supply line which can be connected to a supply of compressed gas or to the atmosphere.
The various features of novelty which characterize the invention are pointed out withe particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention .